Supervisor(s)
:

Byrne, James M.

Abstract
:

A modelling approach focused on snow hydrology was developed and applied to project
future changes in spring streamflow volumes in the St. Mary River headwaters basin,
Montana. A spatially distributed, physically-based, hydrometeorological and snow mass
balance model was refined and used to produce snow water equivalent (SWE) and
rainfall surfaces for the study watershed. Snowmelt runoff (SR) and effective rainfall
runoff (RR) volumes were compiled for the 1961-2004 historical period. A statistical
regression model was developed linking spring streamflow volume (QS) at Babb,
Montana to the SR and RR modelled data. The modelling results indicated that SR
explained 70% of the variability in QS while RR explained another 9%.
The model was applied to climate change scenarios representing the expected range of
future change to produce annual QS for the period 2010-2099. Compared to the base
period (1961-1990), average QS change ranged from -3% to -12% for the 2020s period.
Percent changes increased to between -25% and -32% for the 2050s, and -38% and -55%
for the 2080s. Decreases in QS also accompanied substantial advances in the onset of
spring snowmelt. Whereas the spring pulse onset on average occurred on April 8 for the
base period, it occurred 36 to 50 days earlier during the 2080s. The findings suggest that
increasing precipitation will not compensate for the effects of increasing temperature in
watershed SWE and associated spring runoff generation. There are implications for
stakeholder interests related to ecosystems, the irrigation industry, and recreation.